The invention herein described relates generally to aircraft landing gear and, more particularly, to an integrated wheel, brake and axle that is particularly adapted for an all-electric aircraft braking system.
Known in the prior art are aircraft wheel and brake assemblies including a non-rotatable wheel support, a wheel mounted to the wheel support for rotation, and a brake disk stack having front and rear axial ends and alternating rotor and stator disks mounted with respect to the wheel support and wheel for relative axial movement. Each rotor disk is coupled to the wheel for rotation therewith and each stator disk is coupled to the wheel support against rotation. A back plate is located at the rear end of the disk pack and a brake head is located at the front end. The brake head houses a plurality of actuator rams that extend to compress the brake disk stack against the back plate. Torque is taken out by the stator disks through a static torque tube or the like.
Electrically actuated aircraft brakes of various configurations are known, as exemplified by U.S. Pat. Nos. 4,381,049, 4,432,440, 4,542,809 and 4,567,967. The brake assemblies shown in these patents include electric motors which respond to an electrical control signal to effect rotation of a ring gear member which interacts through a plurality of balls to drive a linearly movable ram member into-contacting engagement with a brake disk stack to effect compression thereof and braking of a wheel.
In U.S. Pat. No. 4,596,316, another configuration of an electrically actuated brake uses a roller screw drive wherein a ring gear member interacts through a plurality of roller screws to drive a ram member into engagement with the brake pressure plate to effect compression of the brake disk stack for braking action. A plurality of electric motors and their associated pinions drive a ring gear into rotation and the plurality of roller screws effect linear axial movement of the ram member.
In U.S. Pat. No. 4,865,162, a further electrically actuated aircraft brake employs a roller screw drive mechanism driven by an electric torque motor through a gear drive associated with either the screw or the nut of the roller screw drive mechanism. Rotation of the gear drive by the torque motor moves the other one of the screw or nut into axial engagement with a brake disk stack to compress the stack for braking. A plurality of the roller screw drive mechanisms and respective gear drives and torque motors are mounted in a balanced arrangement about the axis of the wheel to apply and release a brake pressure force on the brake disk stack in response to an electrical control signal to the torque motors.
One advantage of an all-electric braking system is the elimination of the need for hydraulic fluid, and the associated fluid lines, pumps, etc. However, most attempts today at designing an all-electric braking system have been to fit the electric braking components into a conventional hydraulic braking system design structure, including for example a torque tube and/or torque plate back leg. The problem to be solved is the design of an all-electric braking system that provides performance equal if not superior to existing systems (more robust and dynamically stable structure, more effective cooling, improved torque transfer, improved controllability, better predictability and dynamic response, etc.) while at the same time reducing the overall weight and/or package size of the braking system, number of parts.
The present invention approaches the design of an all-electric braking system in a radically different manner, with attendant advantages over prior braking systems. This is accomplished by integrating the wheel, brake and axle structures, as opposed to such components being treated as separate design components. Moreover, it has been discovered that features of the invention, while originally conceived in the context of providing a superior all-electric braking system, have application to a hydraulic braking system as well.
According to one aspect of the invention, a wheel and brake assembly comprise a tubular axle, and a wheel hub rotatably mounted interiorly of the tubular axle and accessible at an axial end thereof for mounting of a wheel thereto. A wheel having a web and an outer peripheral rim can be telescopically mounted on an end of the wheel hub at a center hole in the web.
In one embodiment, the wheel hub is mounted for rotation by axially spaced apart inboard and outboard bearings. The inboard bearing is captured between axially opposed stepped shoulders on the axle and wheel hub, and the outboard bearing is captured between axially opposed stepped shoulder on the wheel hub and an axle retainer removably secured to the axle. The wheel web may have a tubular projection bearing against an outer race of the outboard bearing.
In an embodiment, a fan is located interiorly of the axle and coupled to the wheel hub for rotation therewith. The wheel hub and axle may have openings therein for passage of air into the interior of the wheel hub. The fan preferably has an exhaust outlet opening to the inboard end of the axle, and a preferred type of fan is an axial vane fan. The fan may be located in a cowling have a reduced diameter portion defining with an interior surface of the axle a protected region for housing a sensor.
In an embodiment, a brake disk stack, having front and rear axial ends, includes alternating rotor and stator disks mounted with respect to the wheel support and wheel for relative axial movement. Each rotor disk is coupled to the wheel for rotation therewith and each stator disk is coupled to the axle for support against rotation. In a preferred arrangement, the wheel web functions as a back pressure member for applying force to the outboard end of the disk stack. The wheel web may have mounted thereon a plurality of disk engaging members, preferably in the form of finned cones.
Further in accordance with the invention, the wheel and brake assembly comprises an actuator assembly supported on the wheel support inboard of the brake disk stack. The actuator assembly may be telescopically mounted on the axle. A preferred actuator assembly includes a housing, with the stator disks coupled to the actuator housing by at least one spline bar coupled to the actuator housing, and the rotor disks coupled to the wheel hub by at least one spline bar coupled at one end to the wheel hub.
In an embodiment, the actuator assembly includes a plurality of actuator modules independently removably mounted to the wheel support, and the actuator modules preferably are electromechanical actuators.
In an embodiment, the actuator modules are mounted to a common support housing telescoped over the axle, and the axle and support housing have at least one interengaged spline and groove